Biology subjects

Parrish, T.

Publications and source records attributed to Parrish, T..

3 recordsLinked to original sources

bioRxiv2026

Therapeutic acute intermittent hypoxia does not alter whole-brain cerebrovascular function in healthy individuals

Acute intermittent hypoxia (AIH) therapy is a promising intervention known to elicit beneficial neuroplasticity. It has been suggested that AIH may also modulate cerebrovascular function, yet the cerebrovascular effects of specific therapeutic intermittent hypoxia protocols remain poorly characterized. Understanding whether AIH results in favorable or adverse cerebrovascular changes is critical in establishing the safety of AIH treatments in populations with elevated cerebrovascular risk. This study investigated cerebral blood flow, cerebrovascular reactivity to hypoxia, and blood pressure effects in a sham-controlled crossover trial (NCT05164705). Healthy young adults (n=18) completed three-week arms of AIH (12 sessions, 15 cycles of 60 seconds hypoxia alternated with 60 seconds normoxia) and sham (6 sessions, normoxia) treatments; phase-contrast and arterial spin labeling magnetic resonance imaging were used to quantify whole-brain and regional cerebral blood flow and hypoxic cerebrovascular reactivity. Blood pressure was measured acutely (before and after each intervention session) and longitudinally (before and after 3 weeks of treatment). AIH treatment did not significantly alter whole-brain resting cerebral blood flow or cerebrovascular reactivity to hypoxia. Blood pressure was unaffected by the treatment acutely or longitudinally. Voxel-wise analysis identified modest regional perfusion increases in the frontal pole, postcentral gyri, and precentral gyri with AIH relative to sham. Significant variability between subjects and between sessions in the hypoxic burden delivered with this AIH protocol was also identified. Overall, this three-week therapeutic AIH protocol produced minimal sustained hemodynamic changes in healthy young adults. The insights from this trial lay a foundation for safely expanding access to this promising rehabilitative intervention in clinical populations.

physiology↗

bioRxiv2020

Geometric deep learning on brain shape predicts sex and age

The complex relationship between the shape and function of the human brain remains elusive despite extensive studies of cortical folding over many decades. The analysis of cortical gyrification presents an opportunity to advance our knowledge about this relationship, and better understand the etiology of a variety of pathologies involving diverse degrees of cortical folding abnormalities. Surface-based approaches have been shown to be particularly efficient in their ability to accurately describe the folded sheet topology of the cortical ribbon. However, the utility of these approaches has been blunted by their reliance on manually defined features in order to capture all relevant geometric properties of cortical folding. In this paper, we propose a deep-learning based method to analyze cortical folding patterns in a data-driven way that alleviates this reliance on manual feature definition. This method builds on the emerging field of geometric deep-learning and uses convolutional neural network architecture adapted to the surface representation of the cortical ribbon. MRI data from 6,410 healthy subjects obtained from 11 publicly available data repositories were used to predict age and sex via brain shape analysis. Ages ranged from 6-89 years. Both inner and outer cortical surfaces were extracted using Freesurfer and then registered into MNI space. Two gCNNs were trained, the first of which to predict subjects self-identified sex, the second of which to predict subjects age. Class Activation Maps (CAM) and Regression Activation Maps (RAM) were constructed to map the topographic distribution of the most influential brain regions involved in the decision process for each gCNN. Using this approach, the gCNN was able to predict a subjects sex with an average accuracy of 87.99% and achieved a Persons coefficient of correlation of 0.93 with an average absolute error 4.58 years when predicting a subjects age.

neuroscience↗

bioRxiv2020

Evidence for immediate enhancement of medial-temporal lobe memory processing by network-targeted theta-burst stimulation during concurrent fMRI

The hippocampus supports episodic memory via interaction with a distributed brain network. Previous experiments using network-targeted noninvasive brain stimulation have identified episodic memory enhancements and modulation of activity within the hippocampal network. However, mechanistic insights were limited because these effects were measured long after stimulation and therefore could have reflected various neuroplastic aftereffects with extended timecourses. In this experiment with human subjects of both sexes, we tested for immediate stimulation impact on encoding-related activity of the hippocampus and immediately adjacent medial-temporal cortex by delivering theta-burst transcranial magnetic stimulation (TBS) concurrent with fMRI, as an immediate impact of stimulation would suggest an influence on neural activity. We reasoned that TBS would be particularly effective for influencing the hippocampus because rhythmic neural activity in the theta band is associated with hippocampal memory processing. First, we demonstrated that it is possible to obtain robust fMRI correlates of task-related activity during concurrent TBS. We then identified immediate effects of TBS on encoding of visual scenes. Brief volleys of TBS targeting the hippocampal network increased activity of the targeted (left) hippocampus during scene encoding and increased subsequent recollection. Stimulation did not influence activity during an intermixed numerical task with no memory demand. Control conditions using beta-band and out-of-network stimulation also did not influence hippocampal activity or recollection. TBS targeting the hippocampal network therefore immediately impacted hippocampal memory processing. This suggests direct, beneficial influence of stimulation on hippocampal neural activity related to memory and supports the role of theta-band activity in human episodic memory. Significance StatementCan noninvasive stimulation directly impact function of indirect, deep-brain targets such as the hippocampus? We tested this by targeting an accessible region of the hippocampal network via transcranial magnetic stimulation during concurrent fMRI. We reasoned that theta-burst stimulation would be particularly effective for impacting hippocampal function, as this stimulation rhythm should resonate with the endogenous theta-nested-gamma activity prominent in hippocampus. Indeed, theta-burst stimulation targeting the hippocampal network immediately impacted hippocampal activity during encoding, improving memory formation as indicated by enhanced later recollection. Rhythm- and location-control stimulation conditions had no such effects. These findings suggest a direct influence of noninvasive stimulation on hippocampal neural activity and highlight that the theta-burst rhythm is relatively privileged in its ability to influence hippocampal memory function.

neuroscience↗